Occupant detection system

Abstract

An occupant detection system including an electrostatic sensor, a determination section and a heater is disclosed. The electrostatic sensor includes an electrode arranged inside a seat of a vehicle and configured to generate a weak electric field. The electrostatic sensor outputs an output value associated with the weak electric field. The determination section supplies voltage to the electrode, and performs an occupant determination to determine an occupant on the seat based on the output value of the electrostatic sensor. The heater is inside the seat, and is arranged in parallel with or on a lower side of the electrode. Before performing the occupant determination, the determinations section determines whether or not the heater has a disconnection fault based on the output value of the electrostatic sensor.

What is claimed is: 
     
       1. An occupant detection system comprising:
 an electrostatic sensor that includes an electrode arranged inside a seat of a vehicle and configured to generate a weak electric field, wherein the electrostatic sensor outputs an output value in accordance with magnitude of the weak electric field or in accordance with change in the weak electric field, wherein the output value is outputted as one of a current output and a voltage output; 
 a determination section that supplies voltage to the electrode, and performs an occupant determination to determine an occupant on the seat based on the output value of the electrostatic sensor; and 
 a heater that is inside the seat, and is arranged in parallel with or on a lower side of the electrode, wherein the heater includes an electric conductor to heat up by a current flowing in the electric conductor, 
 wherein: 
 before performing the occupant determination, the determination section determines whether or not the heater has a disconnection fault based on the output value of the electrostatic sensor. 
 
     
     
       2. The occupant detection system according to  claim 1 , wherein:
 the determination section determines that the heater has the disconnection fault when the output value of the electrostatic sensor is smaller than a preset threshold. 
 
     
     
       3. The occupant detection system according to  claim 2 , wherein:
 the electrode of the electrostatic sensor is provided as a plurality of electrodes including a main electrode, a sub electrode, and a guard electrode; 
 the sub electrode is arranged apart from and adjacent to the main electrode; 
 the guard electrode is arranged apart from and below the main electrode so that the guard electrode is opposed to the main electrode; and 
 when the weak electric field is generated from the main electrode, the sub electrode and the guard electrode, the determination section uses the output value from the sub electrode as the output value of the electrostatic sensor to determine whether or not the heater has the disconnection fault. 
 
     
     
       4. The occupant detection system according to  claim 2 , wherein:
 the electrode of the electrostatic sensor is provided as a plurality of electrodes including a main electrode, a sub electrode, and a guard electrode; 
 the sub electrode is arranged apart from and adjacent to the main electrode; 
 the guard electrode is arranged apart from and below the main electrode so that the guard electrode is opposed to the main electrode; and 
 when the weak electric field is generated from the main electrode and the guard electrode, the determination section uses the output value from the main electrode as the output value of the electrostatic sensor to determine whether or not the heater has the disconnection fault. 
 
     
     
       5. The occupant detection system according to  claim 2 , wherein:
 the electrode of the electrostatic sensor is provided as a plurality of electrodes including a main electrode, a sub electrode, and a guard electrode; 
 the sub electrode is arranged apart from and adjacent to the main electrode; 
 the guard electrode is arranged apart from and below the main electrode so that the guard electrode is opposed to the main electrode; and 
 when the weak electric field is generated from the main electrode, the sub electrode and the guard electrode, the determination section uses the output value from the guard electrode as the output value of the electrostatic sensor to determine whether or not the heater has the disconnection fault. 
 
     
     
       6. The occupant detection system according to  claim 1 , wherein:
 the determination section compares the output value of the electrostatic sensor with a preset threshold to determine whether or not the output value of the electrostatic sensor is smaller than the preset threshold; 
 upon elapse of a predetermined period from a time when the determination section determines that the output value of the electrostatic sensor is smaller than the preset threshold, the determination section again compares the output value of the electrostatic sensor with the preset threshold to determine whether or not the output value of the electrostatic sensor is smaller than the preset threshold; and 
 the determination section determines that the heater has the disconnection fault when a number of consecutive times the determination section determines that the output value of the electrostatic sensor is smaller than the preset threshold reaches a preset number of times. 
 
     
     
       7. The occupant detection system according to  claim 1 , wherein:
 the electrode of the electrostatic sensor is provided as a plurality of electrodes including a main electrode, a sub electrode, and a guard electrode; 
 the sub electrode is arranged apart from and adjacent to the main electrode; 
 the guard electrode is arranged apart from and below the main electrode so that the guard electrode is opposed to the main electrode; and 
 when the weak electric field is generated from the main electrode, the sub electrode and the guard electrode, the determination section uses a ratio of (i) the output value from the main electrode to (ii) the output value from the sub electrode to determine whether or not the heater has the disconnection fault. 
 
     
     
       8. The occupant detection system according to  claim 1 , further comprising:
 an alarm that informs the occupant of an abnormality when the determination section determines that the heater has the disconnection fault, 
 wherein: 
 upon determining that the heater has the disconnection fault, the determination section stops the occupant determination.